300 Bulletin American Museum of Natural History. [Vol. XX\'II, 



itive characters, such as the dental formula, pentadactyly, the general 

 characters of the carpus and tarsus. Some other Placental orders retain 

 more or less of these primitive characters, but they are separated from the 

 Creodonts and Insectivores by well marked specializations, such as the 

 reduction of the dental formula or the hypertrophy of particular parts. 



The l-jpotyphlous Insectivora also occasionally foreshadow the Carniv- 

 ora in their more or less imperfect adaptations to carnivorous habits. 

 Under this head may be mentioned first the development of a semi-carnassial 

 fourth upper premolar in Erinaceus and secondly the many carnivorous 

 features of Centeies, such as the long canines, the broad mandibular coronoid, 

 the broad blade of the scapula, the long skull resembling that of Hyosnodon. 



Additional resemhlances between Insectivores and Carnivores. In his 

 description of the skull of Limnocyon, a Middle Eocene member of the 

 Oxyjenidffi, Dr. Wortman (1902, pp. 202-203) says: "... the position of 

 the posterior lacerated foramen is posterior and external to the periotic, as 

 in the Insectivora, and not postero-lateral, as in the Carnassidentia ; the en- 

 tocarotid enters the tympanic chamber and divides in a manner similar to 

 that of the modern Insectivora, the main branch grooving the outer lateral 

 aspect of the periotic, in front of, and below the fenestra ovalis, the other 

 passing between the crura of the stapes and thence into the brain case . . . . " 



The Creodonta seem to be characterized usually by the presence of an 

 alisphenoid canal, which occurs frequently in the Insectivora but never in 

 the Carnivorous Marsupials and where this is absent (as in Sinopa agilis) 

 the forward course of the ectocarotid is marked by a slight groove in the 

 alisphenoid (Wortman, 1902, p. 440). A similar variability of the alisphen- 

 oid canal is observed in Erinaceus. In this form there is also a transverse 

 venous canal leading into the antrum of the basisphenoid (Wortman, I. c.) 

 and this is a point of similarity not only to the opossum but also to Solenodon 

 (antea, p. 243). The optic foramen is always separate from the foramen 

 lacerum anterius, as it is in the most primitive Lipotyphlous Insectivores. 



Characters separating the Creodonta from the Insectivora. The known 

 Creodonta diflPer from the known lyipotyphlous Insectivora in the following 

 characters : 



(1) Apart from the Oxycl{enidfe, which may possibly be Insectivores 

 (Matthew), the Creodonts all exhibit advanced carnivorous adaptations in 

 the dentition and skull. The gap between the two orders is partly bridged 

 over by Pantolestes and Palcposinopa, Eocene Insectivores with many 

 Creodont features in the skull (Matthew^, 1909). 



(2) The Creodonts are more progressive than the Lipotyphlous Insecti- 

 vores in several features of the skeleton : (a) The scapula so far as known 

 has a very broad prespinous fossa and relatively shallower blade — a car- 



